Marine structure

ABSTRACT

Marine structure with one or more suction piles for embedment into the subsea bottom and with buoyancy sufficient such that the structure can be transported over water independently floating, including in an upright position, wherein the buoyancy is concentrated near the suction piles, and may be substantially in line with the suction piles, and wherein the buoyancy is such that if the suction piles touch the subsea bottom with their undersides, at least part of the buoyancy projects above the water surface.

BACKGROUND OF THE INVENTION

The invention is concerned with a marine structure, a suction pile and amethod for installing a marine structure. The invention is particularly,though not exclusively, directed to the application of so called“minimal platforms”.

DESCRIPTION OF THE RELATED ART

It is common to position a marine structure pre-assembled or in separateparts onto one or more barges or pontoons in a harbour and then tug saidpontoons to the location of destination, whereafter the structure islifted from the pontoons with the aid of a separate hoisting device andis then the structure is installed on the subsea bottom with the aid ofthat device, wherein prior to or after installing the structure onto thesubsea bottom, a foundation therefor is made with the aid of a separatefoundation pile ramming device.

Suction piles and their way of installing are o.a. known fromGB-B-2300661 and EP-B-0011894, which desclosures are enclosed here byreference. Briefly, a suction pile is a thin walled steel cylinder,closed at at least one longitudinal end, that is located on the subseabottom with the opposite end and penetrates the subsea bottom with theaid of a suction created within the cylinder. The creation of thesuction can be with the aid of a suction source, such as a pump, beingon, or close to or at a distance (e.g. above the water surface, e.g. ata vessel) from the suction pile. The applied level of the suction can bee.g. at least substantially constant, smoothly increase or decrease orelse pulsate, for which there are convenient means; for an e.g.pulsating level a possibly in the suction pile integrated pressureaccumulator that is intermittendly connected to the inner space of thecylinder. After use, the suction pile can easily be removed by creatingan overpressure within the cylinder, e.g. by pumping in (sea) water.

SUMMARY OF THE INVENTION

According to one aspect the invention proposes to make the marinestructure self floating and self foundating by providing it withbuoyancy and one or more suction piles. So the hoisting device and thefoundation plant can be eliminated. Preferably the structure hasbuoyancy of its own, e.g. obtained by the with the structure integratedappliance that is designed to, once the structure is installed, ballastthe structure. Buoyancy can also be obtained from the suction pile,which for that can be provided with a floater. Said own buoyancy ispreferably such that it is substantially contributing to the requiredbuayancy to make the structure self floating. It is preferable, if thebuayancy can be at least substantially decreased for installationpurposes. By e.g. filling the one or more floating bodies with ballast,like water. Therefor it is convenient, to provide the structure withmeans for admitting and possibly removing of ballast, such as betweenthe closed and open position switchable shutter valves in a watersupplying respectively water venting opening to a ballast tank.

Since the structure is self floating and is provided with one or moresuction piles, removal after use is made easier. On the one hand in thatby pressing out the suction pile, the anchoring of the structure to theunderwater bottom can be removed. On the other hand in that thestructure can independently rise to the water surface by the (possiblyregained) buoyancy.

The marine structure will typically be relatively small in thisconnection, e.g. a production platform with appliances. Because of itsown weight, such a marine structure is designed to be used with afoundation of pile bodies to be rammed into the ground. Apart from thesuction piles, such marine structure has, preferably, no floatingbodies, neglecting parasitic floating bodies like ineviatbly present airfilled spaces, such as frame tubes. The marine structure referred tohere typically will weigh not more than about 50 tonnes.

Now it is no longer necessary to position the marine structure onto abarge for transport over water. This offers further advantages since themarine structure does not need to be lifted from the barge by a hoistingdevice. If the suction pile offers at least part of the requiredbuoyancy, the marine device can be provided with fewer floatingstructures especially provided for said purpose, or such floatingstructures can even be eliminated.

As such, savings of costs, time, energy, environment and materialarepossible and one can also work safer.

According to another aspect, the invention proposes to use the suctionpile, or part thereof, as floating body of which the buoyancy ispreferably adapted to keep itself floating. In this way it is e.g.possible, to take a suction pile independently floating in te water toits final destination, so without help of one or more auxiliary.floaters. Reclaiming such a suction pile is also made easier. On the onehand in that this can free itself independently from the subsea bottomwith its buoyancy, once pressed upwardly but still partly standing inthe subsea bottom. On the other hand since it can rise to the watersurface independently. In particular the buoyancy of the suction pileaccording to the invention is substantially larger than its own weight,e.g. such that the suction pile alone or in combination with one or moreother suctions piles substantially contributes to the marine structurewith which it is integrated. Accordingly the invention proposes toprovide the suction pile with a convenient buoyancy means.

The buoyancy means can be at least substantially comprise a space inopen communication with the surrounding water at its under side, such asthe pressure space of the suction pile, e.g. if the suction pile will atleast as much upright as possible float in the water. If one can keepsaid space free of water to a satisfying level, the desired buoyancy canbe maintained without requiring to delimit this floating space at allsides with respect to the water environment. Said space can therefore.g. be connected to a convenient means, such as for delivering a gasgenerating dry compound into said space, or for delivering into saidspace a pressurised gas, such as a pump, to generate a convenient gaspressure in the suction space and to possibly maintain it against thepressure of the surrounding water. Due to the movements of the floatingsuction pile in the water, it is expected that without countermeasurements this space will be filled more and more with water frombelow. A remedy is to continuously or intermittendly removing of theflowing in water by e.g. refilling said space with gas, for which saidabove mentioned means is/are continuously or intermittendly activated.In this connection it is preferred to integrate this means in an active,preferably automatic, e.g. electronic control circuit wherein said meansis activated in dependency from the detection of the buoyancy of thesuction pile at different times, such as by measuring e.g. the waterlevel or e.g. the gas pressure within said space with e.g. a convenientsensor, outputting its measuring signal to an evaluation devicecomparing the measuring signal with an input value, switching on orletting switching on said means to get back to the initial situationonce a treshold difference value is exceeded.

Application of the above described space in open communication with itssurrounding water has drawbacks in view of ensuring the buoyancy. Its istherefor preferable if said buoyancy provides one or more floatingspaces that are delimited at all sides with respect to the waterenvironment and that are filled with a floating substance, such as airor a gas or some other material of relatively low specific weight. Saidfloating means can comprise e.g. a separate, inflatable, completelyclosed, diafragm type floating body, preferably within the suction pile,e.g. in the suction space. With e.g. a space of the suction pile that isopen at its lower side, use can be made of an airtight bulkhead withwhich said opening can be sealed. If said bulkhead is at leastsubstantially rigid, e.g. of metal, preferably steel, of sufficientthickness, it can withstand a pressure difference between said space andits environment by bearing bending stresses, hoop stresses or acombination of both. Then it is for realising and maintaining thedesired buoyancy not necessary to bring this space to a pressure that issubstantially higher than atmospheric pressure. If the bulkhead issubstantially flexible, e.g. as an elastic or plastic well formablediafragm of e.g. rubber, it can be necessary for obtainig andmaintaining sufficient buoyancy to bring this space to a pressuresubstantially higher than atmospheric pressure.

Concerning a water tight bulkhead at the under side of the suction pile,one can think of the following structural embodiments and ways ofinstalling: The bulkhead is pressed down by a differential gas pressurewithin the floating space onto a bearing projecting inside into thesuction pile and preferably being ring type to ensure sufficient airtightness. After lowering the suction pile it is position onto thesubsea bottom, wherein said bottom raises said bulkhead from its seat.While the suction pile is sucked into the subsea bottom, the bulkheadremains in place onto the subsea bottom, such that the bulkheadeventually arrives close to the top cover of the suction pile. Duringpressing out, the bulkhead eventually comes to rest on its seat near theunder side of the suction pile. The then fast increasing pressure withinthe suction pile due to the sealing action of the bulkhead is anindication that the pressing out is finished.

To bring the floating space to the desired pressure it is prefered thatsaid space is hermetically delimited. It is then preferred, to connectthe floating space with a convenient appliance to feed pressurised gasinto said space.

The meaning of “delimited at all sides with respect to the waterenvironment” here is that a boundary with respect to the surrounding airis not required. The meaning of “hermetically delimited” here is aboundary both with respect to the surrounding water and the surroundingair.

According to a variant that is preferred at this time, the tube likeshell of the suction pile is extended beyond its top cover, such that afloating space is present above said top cover. In this way the lowerside of the floating space is provided by a fixed bottom. To ensure itsbuoyancy, it is allowable if said floating space has an open top, unlessduring floating e.g. the upper edge of the suction pile comes below thewater surface or waves flush over it. With a view to ensuring thebuoyancy under all circumstances, it is however preferable, to make saidtop side water tight, prferably with a ridig cover. The extension partof the shell can be of the same structure as the shell part below thetop cover. However, some other design (e.g. smaller wall thickness)could be used here because of the different mechanical load. Thisextension part could be integrated with the suction pile, or bedisconnectable to be removed from the suction pile after use. The wallof the extension part can be in line with the shell wall of the suctionpile below the top cover, but could also have a larger or smallerdiameter. The floating space within the extension part is preferablyconnected to a water removing means, such as a bilge pump, such thatincoming water can be removed. The extension part preferably provides asubstantial length part of the suction pile, e.g. about half its length.At a total length of about 20 meter, the extension part has a length ofe.g. about 10 meter if the extension part and shell wall of the suctionspace are in line.

The invention is also concerned with a method of transporting a suctionpile over water since it is independently floating in the water, and amethod of transporting a marine structure over water wherein use is madeof one or more suction piles with buoyancy on which the marine structureis substantially floating. Apart from the the invention is concernedwith a method of regaining of a suction pile or marine structurewherein, preferably after pressing out the suction pile from the subseabottom, a floating space of the suction pile is freed from its ballastto get therewith buoyancy such that the suction pile preferably at leastsubstantially can raise independently towards the water surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Next, the invention is illustrated by way of several non-limitingexamples, that are preferred at the moment. In the drawings is:

FIG. 1 a sectional side view of a first embodiment of the suction pileaccording to the invention;

FIG. 2 a side view of a first embodiment of the marine structureaccording to the invention, during tug.

FIG. 3 the side view of FIG. 2, during lowering;

FIG. 4 the top view of FIG. 2;

FIGS. 5a-c a prespective view, of an alternative structure of FIG. 2,during tug (5 a), lowering (5 b) and sucking of the suction pile (5 c);

FIGS. 6-8 alternatives of FIG. 2;

FIG. 9 a top view of FIG. 6;

FIGS. 10-13 a further alternative of FIG. 2;

FIG. 14 still a further alternative of FIG. 2;

FIGS. 15a-c a side view of FIG. 14.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 the different parts are numbered as follows: Suction pile 1(partly embedded into the subsea bottom 2); shell 3 (of the suctionspace 6; diameter 8 m); top cover 4; open under side 5 (of the suctionspace 6); suction space 6; pump 7 (to get the suction space 6 at alowered respectively elevated pressure); connection pipe 8(tocommunicate space 6 and pump 7); power line 9 (to power pump 7); watersurface 10; floating space 11; shell extension 12.

An alternative is as follows (not shown in the drawings): The suctionpile contains an upwardly movable bulkhead, in this example a concreteballast body, suspended from the suction pile such as with one or morecables or different flexible or bending stiff pull and/or push members,which possibly can be shortened and therefore e.g. can be wound onto ane.g. motoric driven winch. In this embodiment the suction space 6 andthe floating space 11 are combined, which is e.g. material saving, butalso limits the total mass and so the required buoyancy. A function ofthis movable bulkhead is to decrease the free opening at the lower sideof the floating space, such that risc of floating medium (such as air)leaking through said opening is at least decreased, e.g. by decreasingthe influence of e.g. extern water currents on the inside of thefloating space. In that case the bulkhead can keep a large clearancewith the walls of the floating space, such that e.g. the risc of wedgingduring moving up and down of the bulkhead is at least small. Forincreased water and/or floatingmedium tightness, a sealant can beprovided between the bulkhead and walls of the floating space, e.g. ofyielding material such as rubber or elastomer. The bulkhead then alsoprovides a hermetic sealed floating space. During floating the bulkheadcan also be flushed by water at merely under side and possibly sides.However, the indicated water level above the bulkhead offers extracushioning of the influence of water currents to the inside of thefloating body.

For lowering it can be advantageous if the buoyancy of the floatingspace 11 can be easily removed, e.g. by a convenient means, such as avalve, possibly remotely opened, with which at some time water oranother ballast means can be admitted into said floating space and/orfloating means (such as the air or the one or more other gasses) can bevented.

The marine structure according to FIG. 2 and 3 has a platform above thewater surface and floating bodies provided by three suction piles. Theplatform can be designed for supporting the exploitation and/orexploration of oil and/or gas. The platform is e.g. 15 meters above thewater surface. Indicated dimensions are in meters. Each suction pile 1has an integrated, preferably rigid ballast body of e.g. concrete, toe.g. provide stability of the complete structure, in particular duringlowering respectively rising. In this example the ballast body islocated near the level of the bulkhead 4. The ballast body is supportedby the bulkhead 4. The pressure point is above the centre of gravity.The air valve 13 is preferably at a high level, the water valve 14 ispreferably at a low level of the floating space 11. The location of thepump 7 can differ, the same counts for the pipe 8. Although the struts15 are flexural stiff elements, particularly tubes, they can possibly beflexural elements, particularly cables or equivalent The struts are eachconnected to a relevant suction pile and the riser 16. In top view thesuction piles are located at the corners of a triangle of which thesides are provided by girder elements 17 fixed to the suction piles. Thesuction piles 17 are provided with connecting means 18 for a tug means19. The cover 20 of the floating space is spherical. Air and electricitylines 21 for pumping air into the floating space respectivelycontrolling the valves 13, 14 and the pump 7 are guided along thestruts. During tow the structure is vertically oriented. The deck canpossibly also be installed onto the mono pile 16 after the suction pilesare embedded into the subsea bottom 2. The platform can possibly bereplaced by appliances for oceanografic and/or morfologic measurements,or as navigation beacon, etc.

In FIG. 6-8 the situation as installed is shown. The alternativeaccording to FIG. 6 differs from FIG. 2 generally in that the girderelements 17 extend at two different levels while the struts 15 areconnected to the mono pile 16 at a lower level. As with FIG. 2, theadjacent suction piles 1 are mutually and each suction pile is fixed tothe mono pile 16 by the girder elements 17 (view also FIG. 5).

FIG. 7 shows how the floating space is devided into a permanent space 11a and a temporary space 11 b above. The temporary floating space 11 bcan be removed easily, e.g. after completion of the installation. Again,the buoyancy is concentrated at the suction piles 1. This embodimentoffers more stability during lowering. During lowering the spaces 11 bmaintain their buoyancy for the longest period; that of the spaces 11 ais decreased at an earlier moment in time. The permanent floating space11 a offers sufficient buoyancy during tow. For stability duringlowering the spaces 11 b preferably project such high, that they stillproject above the water surface 10 if the suction piles 1 contact thesubsea bottom 2 with the under side. FIG. 8 shows how the temporaryfloating space 11 b during lowering becomes more and more distant fromthe suction piles 1, while those spaces 11 b offer buoyancy duringlowering. The spaces 11 b are therefor connected to the structure byextendable pulling elements; in this embodiment provided by cables 30extending from a winch 31 via sheaves 32 to the respective spaces 11 b.In FIG. 7 and 8 the situation during lowering is indicated with phantomlines. The water surface during tow is shown in phantom lines.

FIG. 10 shows of an alternative the situation in the harbour at the cade40. The structure has maximum buoyancy. The deck 100 is in a lowposition. Floating tanks 42 are fixed below the deck 100 and providebuoyancy (air filled). The suction piles 1 provide also buoyancy (airfilled). The draught is therewith small.

During tow at full sea (FIG. 11) the buoyancy of the structure issmaller, e.g. for improved stability. In this case the suction piles 1provide hardly or no buoyancy.

During lowering onto the subsea bottom 2 (FIG. 12), deck 100 and thesuction piles 1 are moved apart. The floating tanks 42 and the suctionpiles 1 also move apart. The suction piles are sucked into the subseabottom 2.

FIG. 13 shows the final situation. The floating tanks 42 have beenremoved. The deck 100 is located higher above the water surface 10. Abearing structure (in this case a “mono pile”) 16 extends from the deck100 towards the subsea bottom 2. The deck 100 is moved along the monopile. Said moving can be done by a lifting or jacking system.

The suction piles 1 are maintained in mutual position by couplingstructures 17, and via supporting structures they bear the bearingstructure 16. In the embodiment shown both elements 15 and 17 arebending stiff inclined respectively horizontal arms. During floatingtransport the floating tanks 42 are preferably located between saidelements 15 and 17.

FIG. 14 shows in side and top view a marine structure that, onceinstalled, completely disappears in the water (subsea structure, e.g.template). It is equipped with appliances for oil and/or gas productionand is connected to an already drilled production well. The floatingtanks 42 are located in the indicated positions.

FIG. 15a-c shows three different steps for installing the subseastructure. Firts it is towed (FIG. 15a). Next the ballast tanks 42 arefilles, wherein with one or more pulling cables the stability is ensured(15 b). Finally the suction piles 1 are sucked into the subsea bottom.

The invention also covers embodiments that are developed by combiningone or more aspects of an embodiment described in here with one or moreapects of one or more of the other embodiments described in here. Inthis respect a possible embodiment is wherein the usually open underside of the suction pile is fluid tight sealed with a bulkhead, whilethe suction pile is extended above the top cover, such that the suctionpile has two separate floating spces and so an increased buoyancy.According to a further alternative a floating space can be provided byfoam with closed cells, e.g. individual globules of styropor with each adiameter of e.g. about 3 mm, with which the suction space could befilled, the purpose of which is that it is removed, e.g. by pumping, toremove the buoyancy to e.g. lower the suction pile. Such foam,particularly if its is sufficient rigid, in combination with a yieldingbulhead, requires no provision and maintaining of an over pressurewithin the floating space. Such rigid foam can be maintained in positionwithin the floating space by a grid with sufficient fine mesh, whereinsaid grid provides e.g. the boundary with the water of air surroundings.Each foam cell can be viewed as an hermetically sealed floating space inthis, case.

A marine structure with more, e.g. with four, or less than three suctionpiles is also feasible.

The invention is also concerned with the application of the suction pilefor providing the foundation of support of a body, such that the suctionpile is exposed to both a load pressing it into the subsea bottom and aturn, roll or pitch torque from the supported body. Prior toinstallation in the subsea bottom, the suction pile can be irremovablyconnected with the structure to be carried, e.g. be connected thereto byweld joints. However it is preferable from the view point of e.g.installation, to provide the suction pile with coupling means allowingafterwards coupling of the suction pile with the structure to becarried, e.g. after the suction pile. is positioned on the subsea bottomand possibly has lowered itself into the subsea bottom to the desireddepth, or an intermediate depth. Said coupling means are e.g. one ormore flanges with bolts and nuts, known as such. A more advantageouscouling means at the suction pile is adapted to remotely and/orautomatically make the mechanical coupling with the structure to besupported , e.g. with one or more moving parts for hooking or snappingtogether with counter parts at the structure to be supported, or withone or more parts with which moving parts at the counter-coupling partof the structure to be supported can be brought to a load bridgingengagement. Such coupling means are e.g. known as such in the field ofload carrying coupling of a marine structure with a pile rammed into thesubsea bottom, which is substantially more slender than a suction pileand has no provisions to be sucked into the subsea bottom. The couplingmeans are preferably adapted for transmitting a preferably substantialpulling or pushing force and/or substantial torque. Said torque can comefrom a load exerted onto the structure to be supported and trying toturn it around an upright and/or one or two orthogonal axes, in respectof which the term rotating moment or rotating torque, repsectivelytilting moment or tilting couple, respectively pitching moment orpitching torque is used here. If the suction pile is applied in a singlepile foundation with only one suction pile, e.g. for supporting astructure located under water such as a so called template or drillingtemplate (mass e.g. 20 tonnes), or e.g. for supporting a structureextending above water and resting in the subsea bottom, such as a windturbine of e.g. 1 MWatt or more, said coupling means must be adaptedboth for transmitting substantial compression forces and substantialtilting, pitching, and rotating moments.

It will be obvious to the skilled person, how strong the coupling meanshave to be designed to safely transmit the compression forces an/ortorques. In that case the skilled person can e.g. find a basis in thecoupling between the known pile rammed into the subsea bottom and thestructure to be supported.

Apart from these coupling means the suction pile can have appliances forerg. hoisting of the suction pile or connection to a suction or pressuresource and possibly one or more valves to selectively close the suctionspace within the suction pile.

As such the invention also provides a novel suction pile with appliancessuch that it is adapted for supporting materials or devices of equipmentof some type and a predetermined mass of preferably at least about 5000kg that are used for all kinds of applications in or above water, indeedor not in connection with exploitation of minerals such as oil or gas,e.g. bodies that were until now supported by one or more piles rammedinto the subsea bottom.

The invention offers one or more of the following advantageous: ease ofuse, ease of regaining the suction pile, cheap installation of thesuction pile, possibility of first installing the foundation and thenthe body to be supported, robustness, more reliable foundation, improvedbearing of compression forces and/or rotating or pitch or tiltingmoments/torques such that the foundation can be simplified undercircumstances (e.g. one suction piles in stead of two ramming piles,e.g. to prevent the structure to be supported from turning around itsshaft), ease of installation due to the possibility to, e.g., locate thebody to be supported onto the e.g. upright floating or (in shallowwater) onto the subsea bottom positioned or possibly partly into thesubsea bottom penetrated suction pile while subsequently taking the bodyto be supported to the desired level since the suction pile penetratesfurther into the subsea bottom (and vice versa for regaining the body tobe supported).

It is appreciated that with the novel application the suction pile, andtherewith its coupling means, can also be exposed to a tension load,e.g. from the body to be supported and/or since the suction pile alsoserves as an anchor for some different, non-bearing body.

So the invention is according to the enclosed claims.

What is claimed is:
 1. A self-floating and self-foundating marinestructure floating in a body of water and comprising: a foundation partwith one or more suction piles for embedment into the subsea bottom; anda construction above said foundation part, said construction havinginsufficient buoyancy to keep itself floating, said construction beingconfigured to bear on said foundation part when the marine structure isinstalled into the subsea bottom, the overall structure having buoyancysufficient such that the structure as a whole can be transported overwater independently floating, wherein the suction piles provide buoyancyso that the overall structure at least partly floats by the suctionpiles.
 2. The self-floating and self-foundating marine structureaccording to claim 1, wherein the buoyancy is such that if the one ormore suction piles touch the subsea bottom with their under sides, atleast part of the structure remains unsubmerged.
 3. The self-floatingand self-foundating marine structure of claim 1, wherein the structurehas three suction piles at the most, each at a corner of an imaginatedtriangle.
 4. The self-floating and self-foundating marine structureaccording to claim 1, wherein at least a part of the constructionremains projecting above the water surface when the marine structure isinstalled into the subsea bottom.
 5. The self-floating andself-foundating marine structure according to claim 1, wherein thestructure slenders upwardly from the one or more suction piles.
 6. Theself-floating and self-foundating marine structure according to claim 1,further comprising a platform that can move up and down.
 7. Theself-floating and self-foundating marine structure according to claim 1,wherein the overall structure is completely submergible.
 8. Theself-floating and self-foundating marine structure of claim 1, whereinthe structure is transportable in the upright position.
 9. Theself-floating and self-foundating marine structure of claim 1, whereinthe buoyancy is concentrated in line with the one or more suction pilesthere above.
 10. The self-floating and self-foundating marine structureof claim 1, wherein the structure has a pyramid form.
 11. Theself-floating and self-foundating marine structure of claim 1, whereinthe construction is a platform.
 12. The self-floating andself-foundating marine structure of claim 1, wherein the construction isa template.
 13. A self-floating and self-foundating marine structurefloating in a body of water and comprising: a foundation part with oneor more suction piles for embedment into the subsea bottom; and aconstruction above said foundation part, said construction havinginsufficient buoyancy to keep itself floating, said construction beingconfigured to bear on said foundation part when the marine structure isinstalled into the subsea bottom, the overall structure having buoyancysufficient such that the structure as a whole can be transported overwater independently floating, wherein the suction piles include anupward extension providing buoyancy so that the overall structure atleast partly floats by said extension.
 14. The self-floating andself-foundating marine structure of claim 13, wherein the extension isremovably connected to the suction pile.
 15. The self-floating andself-foundating marine structure according to claim 13, wherein theextension is connected to the suction pile by an extendable cable. 16.The self-floating and self-foundating marine structure according toclaim 13, wherein said suction piles provide no buoyancy.
 17. Theself-floating and self-foundating marine structure of claim 13, whereinthe suction piles provide buoyancy so that the overall structure atleast partly floats by the suction piles, the upward extension isremovably connected to the suction piles, and the suction piles andextensions are configured to be lowered together when lowering andembedding the suction piles in the subsea bottom.
 18. The self-floatingand self-foundating marine structure of claim 17, wherein the extensionsare connected to the suctions piles by extendable cables.
 19. Aself-floating and self-foundating marine structure floating in a body ofwater and comprising: a foundation part with one or more suction pilesfor embedment into the subsea bottom; a construction above saidfoundation part, said construction having insufficient buoyancy to keepitself floating, said construction being configured to bear on saidfoundation part when the marine structure is installed into the subseabottom, the overall structure having buoyancy sufficient such that thestructure as a whole can be transported over water independentlyfloating; and parts providing buoyance so that the overall structure atleast partly floats by said parts, wherein the suction piles and saidparts are configured to be lowered together for lowering and embeddingsaid suction piles in the subsea bottom.
 20. The self-floating andself-foundating marine structure according to claim 19, wherein saidsuction piles provide no buoyancy.